1. Field of the Invention
The present invention relates to an improvement in a wire-cut, electric discharge machine provided with a mechanism for automatically installing a wire electrode on its travelling system.
2. Description of the Prior Art
A wire-cut, electric discharge machine is advantageous in that it is capable of machining, for example, a metal mold of complicated configuration with high accuracy through the use of a thin wire electrode. However, such a machine has the defect of low cutting speed. For substantial reductions of labor expenditures during prolonged machining operations, full automation of the wire-cut, electric discharge machine is desired.
An automatic wire threading mechanism which is suitable for continuous, unattended machining of many independent configurations in the same workpiece has been proposed for wire-cut, electric discharge machining. The arrangement of a prior art example of such a mechanism is shown in FIG. 1. In FIG. 1, reference numeral 1 indicates a workpiece; 1a designates a machining starting hole; 2 identifies a wire serving as a working electrode; 3 denotes a supply reel; 4 represents a tension brake; 5 and 6 show guide rollers; 7a and 7b refer to feed-up rollers; 8 and 9 indicate guides; 10 designates a wire clamp; 11a and 11b identify upper feed rollers; and 12 denotes a take-up reel.
For automatic threading of the wire 2 in FIG. 1, the wire 2 is delivered from the supply reel 3, is drawn across the tension brake 4 and the guide rollers 5 and 6, and is gripped by the two feed-up rollers 7a and 7b to run therethrough into the machining starting hole 1a of the workpiece 1. The wire 2 is further projected upwardly through the workpiece 1, is pulled up by the wire clamp 10 to the upper feed rollers 11a and 11b, and is fed to the take-up reel 12.
Since the automatic wire threading mechanism is designed for unattended operations of the wire-cut, electric discharge machine, the wire threading operation must be dependable. With the conventional arrangement, however, when the wire 2 is brought up by the feed-up rollers 7a and 7b into the machining starting hole 1a after being drawn across the tension brake 4 and the guide rollers 5 and 6, there is the possibility that the wire 2 will be inaccurately inserted into the machining starting hole 1a. Inaccurate insertion makes it difficult to carry out unattended operations of the wire-cut, electric discharge machine. It has recently been shown that such faulty operation is caused by curling of the wire.